Thats a mere blind. A pretence; something ostensible to conceal a covert design. The metaphor is from window-blinds, which prevent outsiders from seeing into a room.

1

Blind as a bat. A bat is not blind, but when it enters a room well lighted, it cannot see, and blunders about. It sees best, like a cat, in the dusk. (See SIMILES.)

2

Blind as a beetle. Beetles are not blind, but the dor-beetle or hedge-chafer, in its rapid flight, will occasionally bump against one as if it could not see.

3

Blind as a mole. Moles are not blind, but as they work underground, their eyes are very small. There is a mole found in the south of Europe, the eyes of which are covered by membranes, and probably this is the animal to which Aristotle refers when he says, the mole is blind. (See SIMILES.)

4

Blind as an owl. Owls are not blind, but being night birds, they see better in partial darkness than in the full light of day. (See SIMILES.)

5

You came on his blind side. His soft or tender-hearted side. Said of persons who wheedle some favour out of another. He yielded because he was not wide awake to his own interest.

6

Lincoln wrote to the same friend that the nomination took the democrats on the blind side.Nicolay and Hay: Abraham Lincoln, vol. i. chap. xv. p. 275.

Blind leaders of the blind. The allusion is to a sect of the Pharisees, who were wont to shut their eyes when they walked abroad, and often ran their heads against a wall or fell into a ditch. (Matt. xv. 14.)